1. Field of the Invention
The present invention generally relates to transmission and reception of real time information over communication networks.
2. Description of the Related Art
Certain types of communication signals conveyed over communication systems have the characteristic of being time delay-intolerant. These signals are typically referred to as real time signals, which have strict time delay constraints. The communication system over which the time delay-intolerant signals are conveyed typically comply with the time delay constraints of such signals. Packet switched communication systems convey packets of real time information and other information to and from various nodes where packets carrying real time information comply with the time delay constraints of such information. Packet switched communication systems are communication systems in which the communication signals are converted into one or more packets that are configured as per the protocol being followed by the communication system. The protocol is a set of rules and procedures for initiating, maintaining and/or terminating communications between any two nodes of a communication system. A protocol is usually part of an established standard promulgated by standards bodies such as industry groups and/or governmental agencies. The owner of the communication system, i.e., a service provider, is usually an entity such as a local telephone company or an Internet Service Provider (ISP) or both that operates, controls and maintains the communication system that provides communication services to users of the system.
A packet typically is a group of bits comprising a header portion that contains signaling information and another portion called the payload, which contains the information being conveyed. Packets also have a trailer portion, which contains error correction information that allows a receiver to determine if the packet is received with errors. The signaling information is used by the protocol to regulate the routing and processing of the packet as it travels within the communication system. The header and trailer portions of a packet represent overhead information. Packets to be transmitted in a packet switched communication system are scheduled by the system and are transmitted as per their scheduled times. The scheduling as well as the actual transmission of packets of real time signals or packets carrying real time information have to comply with the time delay constraints of such signals or information.
Examples of real time signals include voice and video signals, both of which can be conveyed over a packet switched communication system in a certain manner to comply with their time delay constraints. The Internet is an example of a packet switched network; the Internet complies with a suite of IP (Internet Protocol), which routes the transmission of packets. VoIP (voice over IP) is one type of delay-intolerant information that can be conveyed over the Internet. Packets of real time signals have to be transmitted at a constant interval for which they have to be scheduled at a fixed time interval. The fixed time interval is a direct consequence of the time delay constraint of these real time signals. Real time signals such as voice and video signals are generated as a flow of information that have a certain constant rate of information flow, which should not be interrupted. The constant rate of flow ultimately defines a constant time period that elapses between each packet transmission. A transmitter transmits real-time packets at a constant rate and a receiver wants to receive these packets at the same constant rate.
Packet data networks are prone to arbitrary inter-packet delays. To ensure packets arrive at a receiver at a constant rate, communication systems typically have used buffers. However, these buffers, also known as “jitter buffers”, are located within the receiver end-point or at an intermediate point from where onwards the rate of flow of the packets can be ensured. These buffers temporarily store a set of packets before they are transmitted at a desired rate of flow to the receiver.
In wireless packet data networks such as 1×EV-DO(1×Evolution Data Only), 1×EV-DV(1×Evolution Data and Voice), and HSDPA (High Speed Downlink Packet Access), and similar communication systems standards data users are scheduled. In scheduled systems, the available data rate is typically dependent on criteria such as channel availability, channel conditions and user priority; therefore the available data rate or the available frequency at which data can be transmitted may be less than the required data rate for real-time packet transmission. Also, because of the fixed rate transmission of real-time packets, the system is not able to take advantage of higher channel capacity availability. As a result of the aforementioned disadvantages, the capacity of the system is often adversely affected.
What is therefore needed is a technique for conveying (i.e., transmit and/or receive) real time information over a communication system that reduces the adverse effects on capacity and efficiency of the communication system.